Fix spec suite on CI

[solnic]

This makes our spec suite better but I'm doing this because our tests started to fail recently with Excon adapter from webmock trying to mutate an array that is defined in Excon. This led me to discovering that load order of spec_helper is significant and we want to load it as soon as possible to get more consistent environment setup.

So this PR:

• Adds --require spec_helper to .rspec
• Removes all manual requires of spec_helper from sentry-ruby spec suite
• Tweaks puma spec so that it force-loads its patches so that we don't care that sentry-ruby was already required by spec helper (a nice discovery)
• Tweaks Rakefile to define isolated_specs task as a regular RSpec::Core::Task which is another small win here
• Consolidates RSpec opts in .rspec so that we have the same settings when running isolated and regular specs

Not strictly needed but:

• Changed rspec format to progress because it's faster, and you can see various warnings

#skip-changelog

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.60%. Comparing base (4e520fc) to head (ca58eb5).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2640      +/-   ##
==========================================
+ Coverage   94.45%   96.60%   +2.15%     
==========================================
  Files         133      133              
  Lines        5101     5126      +25     
==========================================
+ Hits         4818     4952     +134     
+ Misses        283      174     -109     

Components	Coverage Δ
sentry-ruby	97.34% <ø> (+2.42%)	⬆️
sentry-rails	92.65% <ø> (-3.90%)	⬇️
sentry-sidekiq	95.43% <ø> (+15.66%)	⬆️
sentry-resque	94.44% <ø> (ø)
sentry-delayed_job	94.68% <ø> (ø)
sentry-opentelemetry	99.31% <ø> (+0.68%)	⬆️

see 45 files with indirect coverage changes

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